The present invention is related to generators and in particular to control schemes for suppressing DC link voltage build-up in, generators due to unbalanced short circuit conditions.
In synchronous generators, the generation of an alternating current (AC) output voltage is controlled based on the magnitude of an exciter current provided as an input to an exciter field winding. For instance, in a common configuration, a permanent magnet generator and a rectifier circuit are used to provide a DC link voltage. In turn, the DC link voltage is employed to provide a DC current of a desired magnitude to the exciter field winding. An AC voltage induced in the exciter rotor windings is converted to a DC voltage by a rotating rectifier circuit and provided as excitation to a main field winding. In response to the DC excitation in the main field winding, an AC output voltage is generated in the main armature winding that is then provided to a load. In addition, the output voltage and/or output current of the generator are provided as feedback to a controller that controls the magnitude of the DC current provided to the exciter field winding. In, this way, the output voltage of the generator is maintained at a desired magnitude.
To detect potentially fatal errors (e.g., diode faults in the rotating rectifier), the controller may also monitor the DC link voltage. In response to, an increase, in the magnitude of the DC link voltage, the controller orders a shutdown of the generator. However, problems arise when unbalanced short circuit faults at the output of the generator are transmitted through armature reaction to the DC link voltage. The unbalanced short-circuit fault results in the magnitude of the DC link voltage increasing such that a shutdown of the generator is triggered by a condition in which it is preferable to maintain the operation of the generator. It would therefore be beneficial to prevent the buildup of DC link voltage in response to an unbalanced short-circuit fault to prevent the improper shutdown of the generator.